Just checked on my end with 1999 in MS Edge with Smartscreen on, no errors warnings etc.
Using ESET as firewall/antivirus btw. ESET notices during an update that NZBget.exe is being changed (thats why its called updating) but thats all.
I would suspect an NZB being downloaded/is unpacking has an virus in it, or you have some infection that Windows Defender noticed too late (you mention warning 1 / 59, so something must be definitely wrong, maybe install something like
http://www.avg.com/, run scans hope it clears the infection, save your data, and may even install pc again to be sure you got rid of all those warnings).
Note that Windows Defender is not the holy grail for antivirus/firewall. None offers 100% protection, but the free ones (like AVG) have to be free for some reason. I would go for some paid one, like Norton, Symantec, ESET.